The invention relates to a method for manufacturing a plastic fabric-film composite product, a plastic fabric-film composite and a packaging bag comprising the plastic fabric-film composite.
Plastic fabric composite bags are suitable, in particular, for large containers having a substantial fill volume and a substantial fill weight. As a result of individual, mutually intersecting strips of the film-strip fabric, very large loads can be accommodated by known plastic fabric composite bags. Even in the event of local damage to the plastic fabric or the plastic fabric-film composite, further tearing can be prevented by use of the individual, perpendicularly interwoven strips.
The stability of plastic fabric composite bags also is enhanced by way of the strips, which are usually formed from polypropylene, being stretched, wherein the crosswise arrangement of the individual strips in a weaving process results in the formation of a material which is stable in all directions.
Simple, uncoated packaging bags comprising a plastic strip fabric can be utilized, for example, for the packaging of building products, wherein such packaging bags are then generally closed by sewing or bonding, because the film-strip fabric formed from a thermoplastic plastic cannot be easily heat-sealed.
For challenging packaging's, it is known from WO 2009/033197 A1, for example, to provide the plastic-strip fabric with a cover film which is located on the outside on packaging bags to be formed and is imprinted on its side facing the film-strip fabric, wherein the imprint is then visible through the cover film.
Such a packaging bag combines, to a certain extent, the advantages of a simple fabric bag comprising a film-strip fabric, on the one hand, with the advantages of a film bag, on the other hand. By use of the combination described, a very high load-bearing strength and tear resistance is achieved, while the cover film on the outside of the bag ensures a tight closure and a high-quality appearance.
In the case of such a bag, however, a disadvantage can result whereby the film-strip fabric situated on the inner side is not heat-sealable without any further measures and, therefore, it is difficult to close the packaging bag. Moreover, liquids from the interior of the bag can penetrate at least into the film-strip fabric.
To design the described packaging bag comprising a plastic fabric-film composite to be heat-sealable, it is provided according to EP 2 188 438 B1, WO 95/30598 A1, and DE 2 027 060 A, to provide the film-strip fabric with a molten coating that is then arranged on an inner side of a packaging bag and makes it possible to produce heat-sealed seams there. The molten plastic is extruded onto the film-strip fabric for this purpose. In this case, an advantage also results in that the molten plastic can penetrate intermediate spaces of the film-strip fabric, whereby a particularly reliable and intimate connection of the composite is achieved.
The plastic coating is selected in such a way that the melting and softening temperature lies substantially below the corresponding temperatures of the film-strip fabric, so that the stability of the stretched film strips is not adversely affected by the coating or by a subsequent sealing procedure. Consequently, the material selection for the heat-sealable plastic coating is extremely limited.
Another type of closure of a film bag is known that allows for mitting such a coating. For example, the packaging bag formed from a film-strip fabric can be turned inside-out and can be closed with the aid of adhesive or an adhesive strip. An embodiment of this type is known from WO 01/05671 A1.
In addition to a closure utilizing hot-melt adhesive according to U.S. Pat. No. 4,373,979, simple sewing is also an option.
According to WO 2013/123015 A1, a stepped trimming also can be provided on an upper edge and on a lower edge of the packaging bag, so that the doubled-over ends are more easily closed, for which, for example, a connection by ultrasonic welding and/or hot air can be considered.
A plastic-fabric composite bag is known from US 2013/0040084 A1, which comprises on its inner side a barrier layer that is applied onto the film-strip fabric with the aid of adhesive.
WO 03/074264 relates to a cross-laminate, which comprises two that are adhered to each other. The films themselves each comprise a layer formed from strands situated in parallel to each other.